1. Field of the Invention
The invention is related to electrical insulator components of electrical motors and methods of their installation and more particularly is related to tubular electrical insulators for mounting between the armature shaft and the windings or laminations of an armature in electrical hand tools.
2. Brief Description of the Prior Art
Prior hereto, glass-reinforced polymeric resin insulator tubes have been mounted on the armature shafts of electrical hand tools to provide so-called "double insulation." Phenolic impregnated paper insulating tubes have been similarly used. These prior art insulators are prepared for use on armature shafts of specific diameters by grinding on both the inner and outer surfaces to meet extremely exact tolerance specifications. The armature shafts also are generally milled to meet very close tolerance specifications so that mounted insulator tubes will form a tight frictional engagement with the armature shaft.
The glass-reinforced polymeric resin insulators are generally mounted within the laminations by press fitting to obtain the desired tight frictional engagement. The mating armature shaft is then pressed into the insulator tube. The phenolic impregnated paper insulating tubes are generally installed by bonding the close fitting insulation tube to the armature shaft with an applied cyanoacrylate adhesive. The assembled shaft and insulator are bonded to the laminations by the same adhesive.
Those skilled in the art recognize the shortcomings of the prior art armature insulators and the methods of their installation. For example, the need for grinding the tubular insulators to precise dimensions on both inner and outer surfaces is costly. The need to meet very rigid dimensional specifications in both insulator body and armature shafts increases the potential for rejected components and materials, thereby increasing costs and causing economic waste of our national resources, i.e.; labor, materials and energy. Further, the methods of installation, such as by press-fitting require costly capital expenditures for press-fitting apparatus. Although this particular disadvantage would seem to have been eliminated by installation of the phenolic insulator tubes by bonding with a cyanoacrylate adhesive, this latter method has not achieved a high degree of reliability in effecting a permanent bond, although considerable time and money has been invested in development of the method.
The novel tubular insulators of my invention and the method of their installation eliminate many of the problems and disadvantages of the prior art. For example, the insulators of my invention do not require precise inner or outer diameters and may be mounted on armature shafts having a variety of different diameters and having relatively wide tolerances in dimension. Similarly, the outer dimensions of the insulator tubes need not meet critical dimensional specifications for the distance between laminations. The invention will reduce the inventory of different insulator tube sizes which a manufacturer must presently maintain. Further, the need for critical dimensions in the armature shafts is eliminated and the insulators of the invention may be readily installed on "off-specification" armature shafts, thereby decreasing the rejection rates of components. The method of the invention is also highly reliable.
In addition, the insulated armature shaft prepared according to the method of the invention have improved thermalresistance and improved electrical insulating properties over many of the prior art insulated armatures.